In a known art for such non-contact holder, when a workpiece (work) such as silicon wafers and semiconductor wafers is transferred to a subsequent step or in the same step in its production process, it has been required to prevent dust deposition and damage to the workpieces, increase in the size of the workpieces and decrease in the thickness thereof. However, such requirements have made it significantly difficult to mechanically and directly hold the workpieces for carriage.
To deal with this problem, a non-contact holder has been proposed (for example, see Patent Document 1: Japanese Unexamined Patent Publication No. 2002-64130). In such conventional non-contact holder, air or nitrogen gas is blown to a workpiece at a predetermined pressure to hold the workpiece in no contact state depending on the balance between positive and negative pressures.
In such conventional non-contact holder, however, because jetting flow of a fluid such as air jetted on the workpiece from a jetting port constitutes a swirling flow, in a case of holding the workpiece in the non-contact state (hereinafter, called “non-contacted state”) by one non-contact holder, the workpiece is rotated slightly gradually by the swirling flow of the air and is not held in a stationary state, thus being inconvenient and providing a problem.
In order to solve such problem, as in a panel-type non-contact holder A in FIG. 8, it was necessary to dispose at least two non-contact holders CW and CCW, which produce swirling flows in different directions, for example, a clockwise direction (CW) and a counterclockwise direction (CCW), so as to be adjacent to each other on a panel B.
This non-contact holding unit A, however, requires a plurality of non-contact holders. In addition, two adjacent non-contact holders produce swirling flows that collide with each other and cancel each other on a non-contact holding surface of the workpiece, thereby generating a noise such as wind noise and reducing air supply rate and pressure.
Further, in addition, if the swirling flows produced by the two non-contact holders produce pressure difference (have different pressures), the workpiece rotates by the higher pressure, and accordingly, the air supply rate and pressure to the adjacent non-contact holders CW and CCW must be properly controlled with high accuracy to be substantially uniform.
Even if the pressures of the adjacent swirling flows are substantially uniform, the pressures pushing or pushed to each other act on the workpiece, which causes a strain, and in a case that the workpiece has a thin thickness, the workpiece is undesirably deformed in the thickness direction and vibrated, whereby a noise is caused and the stress is increased, thus being inconvenient.